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Is it possible to effectively use a tado extension kit to replace a three channel controller.

edited November 2019 in Technical Questions

I have underfloor heating downstairs and radiators upstairs. I also have a hot water storage tank upstairs. The timings associated with the firing of the boiler are managed by a three channel controller (Horstmann ChannelPlus H37).

I have installed tado smart thermostats in each room downstairs, set the 'downstairs' channel on my Horstmann controller to permanently on and these work well based on the schedules I have created in the tado app.

I have installed tado smart radiator thermostats upstairs on all the radiators. Again these work well with the schedules I have created in the tado app - HOWEVER - upon setting the 'upstairs' channel on my Horstmann controller to permanently on, in anticipation of the tado radiator thermostats managing the call for heating, the 'heating' actuator for the upstairs area immediately opens and starts the pump next to the boiler. This actuator remains open and the pump continues to circulate water from the boiler to the radiators irrespective of whether or not any of the tado radiator thermostats are calling for heat or not. While this 'theoretically' works, in that the radiators will only actually heat up according to the schedules I have created in the tado app, the heating pump remain permanently on. For example, during the night when I have set the tado radiator thermostats very low (13), the pump keeps on pumping all night.

It had been my intention to continue to control my hot water needs using the third channel on my Horstmann controller, however I have now also purchased a tado extension kit and would like to install this in the hope that I can configure it such that the heating pump only comes on when the radiators are actually calling for heat while it also controls my hot water demands.

Tado have indicated they do not have instructions to replace a three channel controller with an extension kit and have suggested I contact a local electrician to change the wiring.

Has anyone in the tado community successfully 're-wired' the actuators in their system such that a tado extension kit can replace a three channel controller.

Any advice/guidance greatly received.


  • Just by way of follow up ......

    I have now managed to accomplish what I was hoping to. 

    My tado Extension Kit is now in place and is actively controlling my upstairs radiators as well as my hot water supply. Both are operating effectively via the schedules I have set in the tado mobile phone app. In addition, the tado wall mounted smart thermostats are now effectively controlling my downstairs underfloor heating, again via schedules I have set up in the tado mobile app. Key to this however, is that the downstairs underfloor heating and the associated thermostats are not associated with the Extension Kit, but are operating independently of it, and I have simply directly wired (in behind the Extension Kit) the wires controlling this, which was the original channel one on my previous Horstmann three channel controller. My original channels two (upstairs heating) and three (hot water) are now wired in as channel one and two on the tado Extension Kit. The success of this is down to Tado support staff, who at my request, remotely configured the Extension Kit to ignore the downstairs thermostats, and to simply interact with the upstairs radiator thermostats (wirelessly) and the hot water system.

    Having set this up I did, for a number of days, have the ongoing problem that the downstairs actuator would not switch off even when no thermostat was calling for heat and as a consequence, the boiler pump and the downstairs underfloor heating pump, ran continually (24/7). I tried several re-wiring arrangements without success but then I temporarily disconnected all thermostats (seven downstairs and nine upstairs) and reconnected them all again and mysteriously everything now works exactly as it should. When the downstairs thermostats stop calling for heat, the actuator closes and the pump stops. At the same time I can, via the mobile phone app, have any or all (or none) of the upstairs radiators and or hot water, successfully calling for heat. 

    While it has taken me a few weeks (and some cursing) to work it all out, it is now working exactly as it should and exactly as I wanted it to, but of course with the significantly added convenience provided by the tado mobile phone app, allowing me to turn heating on/off to any room from literally anywhere in the world and indeed the additional benefits of the geofencing etc.

  • Hi Cor,

    Hoping you can help, I followed your posts and the situation sounds similar to mine. I have an existing 3 channel ESI programmer and Tado have just said to send everything I've purchased back as it's simply not compatible.

    What you've done sounds like it is though. The bit I'm not quite clear on is when you say "I have simply directly wired (in behind the Extension Kit) the wires controlling this, which was the original channel one on my previous Horstmann three channel controller."

    Does this mean you have an extension kit and thermostat controlling one zone and the hot water and then you've directly wired in a second thermostat to control the second zone? Or have you doubled-up the wiring for zones 1 and 2?

    thanks in advance.

  • Hi jdku2003,

    Before Tado I also had a ESI 3 Channel Programmer; Hot Water; CH 1 for ground floor and CH2 for 1st floor radiators. I also had thermostats in the hall on the ground floor and in the master bedroom for the 1st floor. The thermostats controlled the motorised valves for each floor.

    I now have the following setup; extension kit replacing the ESI programmer, controlling only the hot water. Two smart thermostats replacing the existing thermostats. 5 smart TRVs; 3 on the ground floor and two on the 1st floor. More smart TRVs to come later.

    I asked Tado Support to only allow the extension kit to control the hot water. Each smart thermostat was assigned a floor (zone) along with corresponding smart TRV. Tado support did say I would need an electrician to rewire but being an electrical engineer it was a no brainer to 'swap a wire' at the extension kit. Now the smart thermostats are independent of the extension kit.

    Now when a radiator calls for heat it will ask the smart thermostat assigned to that zone to switch on; which in turn activates the motorised valve for that zone causing the pump and boiler to start.

    I still have a 3 radiators that don't have smart TRVs, they heat up whenever the smart thermostat or a smart TRV calls for heat depending on the zone; 1 on the ground floor and 2 on the 1st floor.

    I hope this helps a little, don't give on Tado.

    Thanks, Sparky

  • Amazing, it sounds like the exact same setup!

    I'm not an electrician so it sounds like I'm going to need one as I don't know what to do with the CH1 and CH2 wires that are currently going into the ESI programmer. I guess they have to be terminated somehow? Wiring the thermostats is simple enough.

    I'll see if I can find a sparky! Thanks for your answer

  • No worries, the thing here is getting Tado support to setup the backend config; zones and smart TRVs. Before the smart TRVs were added I had CH1 and CH2 in the same connection on the Extension kit. On the back of Extension kit is schematic, it's essentially two relays, one for hot water and one for central heating. With two positions, Normaly Open and Normaly Closed. As long as Tado doesn't switch on my CH heating using the Extension kit my setup will continue to work via the smart Thermostats and TRVs.

    On a side note, I live in rental property so any changes I made are very easily reversed.

    Thanks , Sparky
  • Ah ok, I had wondered about putting both zones into one. I can do that simply enough. I've emailed Tado and asked them if they'll do the same for me as they've done for you, fingers crossed they will and not just give the usual answer of "take it all back", which seems a bizarre response.

  • Hi there jdku2003,

    Please accept my apologies. Since resolving my issue and posting above in Dec 2019, I have not revisited this discussion forum until today. Nor did I get any notification or email indicating anyone had commented or questioned my post.

    While it is probably far too late to be of any use to you, I am attaching a schematic diagram, showing how I moved the existing wiring of the Horstmann H37 Channel Plus, and wired those existing wires to the Tado Extension Kit.

    Please note - I am NOT an electrician and I am most certainly NOT advising you or anyone else to implement this solution. All I'll say is I did this in December 2019 and my system (all upstairs radiators, all downstairs underfloor heating and the hot water) has been working perfectly since.

    In the attached schematic (powerpoint) the top part represents the Horstmann and the way the existing wires were attached to it. The bottom part represents the Tado Extension Kit and the way I attached the existing wires to it.

    The 'directly wired' piece that you queried is effectively where multiple wires from the Hosrtmann setup are relocated to a single connector in the Tado setup. Note however, this only worked due to the remote re-configuring that Tado did for me (as described above).

    Hope this is helpful and sorry again for the delayed response.

  • hi @Sparky can you please share your wiring setup for extension kit as I also have ES3247B timer for heating and hotwater.

    From your above description I did get most of it but not 100% sure so some visual image would be nice.

    My understanding is

    • Connect Both zone wire to CH0 of extension kit and connect HW to CH1
    • then request tado support to always keep CH0 on! This way extension kit only control the HW

    is this right?

    can anyone help me with the setup please :( Tado support say they dont support this officially but unofficial its possible! I wish they would publish some guide for such setup with outlining limitation.

    also its been very common to have multiple zone i am surprised tado didn't manage to find official solution.

  • Hi @vjain419 have you replaced the room stats with the Smart Thermostats for each zone and are they wired? This setup only works with Smart Thermostats are Wired / 230v Relay.

    There are two issues:
    If you connect the heating zones to CH OFF (my current setup) and Tado don't make changes to the Extension Kit config when there is a call for heat in either zone, neither zone will heat.

    If you connect the heating zones to CH ON then only one zone will heat and other will only heat when both zones are asking for heat at the same time.

    From my experiences and looking at s-plan wiring diagrams the Central Heating side on the timer supplies power to the room stats, in theory if you connect both heating zones wires to the live at the Extension Kit rather than CH OFF, you shouldn't need Tado to make any changes to the Extension Kit config. The Smart Thermostats then become the controller for each zone as they should be. Depending on your wiring there may be insufficient space in the backplate, you might need looped terminal block.

    I suggest you setup the Internet Bridge, pair everything up then ask Tado to setup the multi room for the Smart Thermostats and the Hot Water. If you have TVRs, get Tado to assign them to the relevant Smart Thermostat zone.

    Photo of my Extension Kit > https://ibb.co/tcJXRdB

    Hope this helps.

    Cheers, Sparky

    If in doubt, seek help from a qualified electrician.
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